Field of the Disclosure
The present disclosure, for example, relates to wireless communication systems, and more particularly to closed-loop power control.
Description of Related Art
Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems. A wireless network, for example a Wireless Local Area Network (WLAN), such as a Wi-Fi network (IEEE 802.11) may include an access point (AP) that may communicate with stations (STAs) or mobile devices, otherwise known as user equipments (UEs). The AP may be coupled to a network, such as the Internet, and may enable a mobile device to communicate via the network (and/or communicate with other devices coupled to the access point).
Some WLAN systems use carrier sense multiple access (CSMA) to share a wireless medium between multiple nodes in a basic service set (BSS). CSMA is a media access control (MAC) protocol in which an AP or wireless station verifies the absence of other traffic on a shared transmission medium before transmitting over the medium. Typically, in a Wi-Fi network, a wireless station that wishes to transmit over the medium performs a clear channel assessment (CCA) to determine whether the medium is idle for a fixed period before transmitting. The fixed period may be a distributed coordinate function (DCF) interframe space (DIFS). If a wireless station determines that the medium is idle (i.e., free) for a time period specified by the DIFS, the wireless station may transmit a first data packet. After waiting for another DIFS, the wireless station may transmit a second data packet if no other traffic occurred on the medium during the DIFS.
A short interframe space (SIFS) burst is a technique that a node may employ to bypass the requirement to have a DIFS between transmitting data packets or any other technique employing an interframe space (IFS) such as point coordination function (PCF) interframe space (PIFS) to maintain control of a channel and prevent other stations from contending for the medium. During a SIFS burst, a wireless station may transmit a series of data packets in close succession. Instead of the data packets being separated by a DIFS, in a SIFS burst the data packets are separated by a SIFS. The SIFS is typically shorter than the DIFS. During a SIFS burst, another node in the BSS has no opportunity to use the wireless medium because a node cannot begin to transmit over the medium until the medium has been quiet for at least the DIFS.
Power control during a SIFS burst has been limited. Open-loop power control techniques are used for Wi-Fi systems, but are inadequate during a SIFS burst. A communication system using an open-loop power control technique may attempt to progressively reduce a power amplifier bias when operating at the highest modulation and coding scheme (MCS) and when a packet error rate (PER) is less than a predetermined threshold. However, these techniques may miscalculate a link budget because the calculations are based on indirect metrics, such as the PER. These open-loop techniques may also be reactive in nature, which may result in PER jumps before recovery actions may be taken to restore power to the transmission. Using these open-loop power control techniques for a SIFS burst may lead to disruption of a SIFS burst due to packet failures. Further, these open-loop power control techniques are often only implemented when the MCS reaches a ceiling.